sensor-mon: Remove unused variable

Fix clang-tidy error:
```
../sensor-monitor/threshold_alarm_logger.hpp:211:25: error: private field 'event' is not used [-Werror,-Wunused-private-field]
```

Signed-off-by: Matt Spinler <spinler@us.ibm.com>
Change-Id: I35ef3a74be5e1db36d39c6ffafbd11e5a784ba87
diff --git a/sensor-monitor/threshold_alarm_logger.cpp b/sensor-monitor/threshold_alarm_logger.cpp
index 54f5a8a..6316dad 100644
--- a/sensor-monitor/threshold_alarm_logger.cpp
+++ b/sensor-monitor/threshold_alarm_logger.cpp
@@ -86,9 +86,8 @@
                               Entry::Level::Informational}}}}}}};
 
 ThresholdAlarmLogger::ThresholdAlarmLogger(
-    sdbusplus::bus_t& bus, sdeventplus::Event& event,
-    std::shared_ptr<PowerState> powerState) :
-    bus(bus), event(event), _powerState(std::move(powerState)),
+    sdbusplus::bus_t& bus, std::shared_ptr<PowerState> powerState) :
+    bus(bus), _powerState(std::move(powerState)),
     warningMatch(bus,
                  "type='signal',member='PropertiesChanged',"
                  "path_namespace='/xyz/openbmc_project/sensors',"